1. Introduction

1.1 Description of LGH Production System

1.1.1 Geographic Distribution

Livestock grazing systems in humid areas (LGH) are most prevalent in South America where countries such as Argentina, Brazil, Columbia, and Paraguay account for 62.6 percent of the agricultural land in the LGH (see Table III.1). China, Australia, and the U.S. account for the remainder with 70 percent of the LGH human population and 18 percent of its agricultural land in China. This category represents about 75 percent of the livestock grazing systems in humid zones worldwide with the remaining 25 percent in Africa. The agricultural land in the LGH is 88 percent pastureland but is rather densely populated at the rate of 1.9 ha/capita overall and 0.5 ha/capita for China.

1.1.2 Livestock Resources

The LGH represents about 13 percent of the world’s pastureland and accounts for 12 percent of the world’s cattle, and 6.4 percent of its sheep and goats (Table III.2). As with the agricultural land, South America accounts for the majority of the LGH cattle (83 percent) and sheep (57 percent). However, most of the goats (57 percent) are found in China. Significant numbers of sheep are found in Australia and China. Livestock feed demand (based on livestock unit equivalents) for the three types of livestock in the LGH comes primarily from cattle (89 percent).

1.1.3 to 1.1.7 (See Sere’s report)

Table III.1 Human Population and Hectares of Arable and Pasture Land in the Livestock Grazing-Humid, Subhumid Tropics and Subtropics Zone (excluding Africa)

		Human Pop. (mill)	% of Natl. Total	Pastureland (mill ha)	% of Natl. Total	Cropland (mill ha)	% of Natl. Total
OECD
North America:
	United States	9.7	3.9	38.8	16.2	5.3	2.8
South Pacific:
Australia		1.5	8.8	44.2	10.6	6.7	14.3
CSA
	Argentina	8.0	24.8	64.0	45.0	12.0	48.0
	Bolivia	2.0	27.4	12.8	48.1	1.0	47.6
	Brazil	30.0	19.9	80.0	43.4	14.0	27.8
	Columbia	7.9	23.0	36.0	89.1	1.5	38.5
	Ecuador	0.7	6.6	1.0	19.2	0.2	11.8
	Mexico	5.5	6.2	16.0	21.5	3.0	13.0
	Nicaragua	1.0	25.6	4.0	74.1	0.3	27.3
	Panama	0.6	25.0	1.0	62.5	0.1	20.0
	Paraguay	4.3	100	21.1	100	2.1	100
	Peru	1.9	8.5	14.0	51.7	0.7	20.6
	Uruguay	1.1	35.3	10.0	74.1	0.3	23.1
	Venezuela	3.0	15.5	8.0	45.2	1.0	31.3
ASIA
	China	180.3	16.2	78.0	19.5	9.0	9.3
Total		257.5		428.9		57.2
% of World LGH		78		71		76
% of World Total		4.7		12.8		4.2

Table III.2. Numbers of Head of Cattle, Sheep, and Goats in the Livestock Grazing-Humid, Subhumid Tropic and Subtropic Zone (excluding Africa)

		Cattle (mill)	% of Natl. Total	Sheep (mill)	% of Natl. Total	Goats (mill)	% of Natl. Total
OECD
North America:
	United States	3.1	3.2	4.1	24.4	0.5	2.6
South Pacific:
Australia		3.9	16.8	19.5	11.5	0.1	16.7
CSA
	Argentina	20.7	41.0	8.0	28.0	0.4	12.1
	Bolivia	2.7	49.1	3.0	39.0	0.6	42.9
	Brazil	58.0	39.4	7.6	38.0	6.0	50.4
	Columbia	14.3	58.6	2.1	84.0	0.6	60.0
	Ecuador	0.8	18.2	0.2	14.3	0.1	33.3
	Mexico	6.8	21.2	1.8	31.0	2.4	23.1
	Nicaragua	0.8	47.1	0	0	0	0
	Panama	0.7	50.0	0	0	0	0
	Paraguay	8.3	100	0.5	100	0.1	100
	Peru	2.0	48.8	5.1	41.5	0.5	29.4
	Uruguay	5.8	66.7	18.0	71.4	0	0
	Venezuela	6.0	45.1	0.2	40.0	0.8	53.3
ASIA
	China	19.4	25.2	11.5	10.1	16.3	16.6
Total		153.3		81.6		28.4
% of World LGH		81.5		75.4*		75.4*
% of World Total		11.9		6.4*		6.4*

* Sheep plus goats

1.2.1 Livestock Resources

Cattle numbers across the entire LGH system were relatively steady over the past decade. Modest declines in the LGH systems of most other countries offset a significantly large increase in Brazilian cattle stocks. Sheep numbers in the LGH declined slightly over the past decade led by significant decreases in Argentina and the U.S. However, these decreases were almost matched by significant increases in sheep numbers in Uruguay and Brazil. Goat numbers increased slightly over the LGH led by significant increases in Brazil and Mexico.

1.2.2 Production Technology, Livestock Use, and Products

Productivity of beef and dairy cattle enterprises is generally improving in the LGH. The improved productivity is primarily due to increased use of crossbreeding and improvements in forage quality through increased use of derived pastures and fertilization. In addition to significant increases in dairy productivity, the number of dairy cows is also increasing.

1.3 Overview of Key Indicators

1.3.1 Direct Indicators

1.3.1.1 Soil Structure

Soil structure is impacted by grazing animals in the upper 25 cm, indicating that it is a near-surface phenomena. As duration of stock density increases soil compaction generally increases, especially in high moisture, early growth conditions. Grazing lands subjected to frequent freeze-thaw or shrink-swell processes mediate negative soil structure impacts. Short-term heavy grazing does not yield measurable impacts on root mass in the soil but has been shown to decrease earthworm activity. Periodic rest from rotational grazing can reverse any negative effects of increased bulk density and reduced infiltration rates with proper stocking and sufficient rest periods. However, long-term heavy grazing impacts are more notable and must be viewed in the context of scale. Nutrients and water patterns flow across and beneath landscapes from a series of sources and sink with grazing serving as a redistribution agent. Grazing per se does not alter systems significantly until landscape features are altered to a point where water, nutrients, organic matter, and sediment loss is accelerated. The challenge for resource managers is to identify threshold conditions which lead to formation of erosion cells causing accelerated soil loss, leaching via lateral flow, increased runoff, and reduced infiltration processes. As long as the erosion constitutes redistribution within the landscape, it does not lead to irreversible degradation. When it reaches the level where there is a net loss of soil from the landscape (via channels, streams, and rivers), degradation becomes evident.

1.3.1.2 Soil Erosion

See Section II-1.3.1.2.

1.3.1.3 Pesticide Residues

The literature indicates that relatively high levels of herbicides can be measured in runoff water from treated rangeland areas immediately after treatment, or after the first precipitation event following treatment. However, there is little evidence that even these initial rates measured are of significant environmental concern. Moreover, the dissipation rates of the compounds are rapid. The key to environmentally safe use of herbicides in the rangeland environment is to ensure that they are used in accordance with the labels for rates of application. When this precaution is followed, little chance for negative environmental impact exists. The use of herbicides for the purpose of altering the composition of vegetation on grazinglands for a variety of objectives is a sound practice. Weeds, including forbs, half-shrubs, or woody plants, can severely reduce forage production on rangelands and derived pastures. In many cases chemicals may be the only practical or economically feasible method to reduce woody and herbaceous weed competition and restore the opportunity for range condition improvement through grazing management.

1.3.4 Carbon Dioxide Balance

One of the major interpretations from the CO₂ hypothesis is that shifts from grasslands to shrublands cannot be fully attributed to mismanagement, as has been frequently espoused in much of the literature. The CO₂ hypothesis suggests that a lack of understanding of the fundamental causes of vegetation dynamics on rangelands has probably been the primary constraint to the development of totally successful approaches to dealing with the range brush and weed problem (Mayeux et al. 1991). The reality of the changes to shrub-dominated ecosystems that have already taken place on many rangeland areas, and with the probability of increasingly competitive advantage to shrubs and broadleaf herbaceous plants, the use of grazing animals more suited to C₃ plants may be warranted. This approach would mean more efficient use of range vegetation could be made by goats and sheep in areas historically grazed totally or predominately by cattle. There may also be bases for consideration of the use of introduced or native animals with higher affinity for shrubs and forbs than domestic livestock. It may also mean significant shifts in grazing management paradigms and the social structure associated with land use. The impact of leaf-eating herbivores may increase as the level of atmospheric CO₂ rises. Furthermore, C₃ weeds may grow faster than C₄ crops of agricultural importance in a CO₂-enriched environment, and vice versa. In unmanaged ecosystems these effects of elevated CO₂ may cause marked changes (Bhattacharya 1993).

1.3.5 Vegetation Ground Cover

Cover of vegetation has been identified as one of the major mediators of raindrop impact and subsequent infiltration rates, runoff levels, and sediment loading. Vegetation structure also impacts light and water interception, competitive interactions between plant species, and habitat structure for animals and insects. Grazing directly impacts vegetation cover through removal of foliage and trampling, indirectly affecting competitive interactions and subsequent species composition. Increasing grazing pressure decreases interception loss, reduces litter turnover and interception losses, increases bareground, and increases raindrop velocity. This results in slower infiltration rates, increased runoff amount and flow rates, and greater sediment loading. Hydrologic thresholds of vegetation cover, where grazing has been noted to have significant impact on hydrologic processes, have been identified to be 300 kg/ha for sodgrass cover and 1000 to 1440 kg/ha for bunchgrass communities in temperate grasslands.

1.3.6 Aboveground Biomass

Grazing-induced modifications of competitive interactions are eventually expressed at the population level through the modification of canopy size, basal area, and tiller/meristem demography of individual plants. Decreases in plant basal area in bunchgrasses are most likely a consequence of the fragmentation of individual plants into smaller units. Populations composed entirely of plants with reduced basal area may be jeopardized by the inability to compete effectively with populations of less severely grazed species and increased susceptibility to extreme abiotic conditions. Grazing impact on aboveground biomass is a function of chosen herbivore mix, numbers of animals for each kind of herbivore, and plant growth patterns relative to temporal and spatial weather events. Species composition change is a relatively rapid response, while changes in annual net primary production are an intermediate response. Soil nutrient loss is a slow, variable response. Aboveground net primary production does not necessarily change when species composition changes and can increase or decrease depending on the replacement species, life-history traits, and the manner in which the continuing grazing pressure or stress affects water and light resources and nutrient cycling rates. Increases in short-term nutrient cycling rates may increase primary production over time periods of years to decades while decreasing large, recalcitrant nutrient pools. Yields of bunchgrass species appear to be slightly reduced (less than 10 percent) with end-of-season utilization levels up to 60 percent. However, yield is negatively impacted in an exponential manner with end-of-season use levels from 60 to 90 percent.

1.3.7 Root Biomass

Defoliation by grazing animals commonly results in cessation of root growth, followed by a period of rapid tillering, but the net effect of defoliation on pasture production depends on the relative growth rate of the sward as well as intensity and frequency of grazing. Suppression of root growth is generally proportional to the intensity and frequency of defoliation. Longevity of roots varies between species and generally is reduced when shoots are defoliated However, the significance of root longevity to plant survival and competition has not been clearly ascertained. Heavy grazing has resulted in higher tiller density but lower root mass than plants in a lightly grazed pastures. The use of species-based criteria in management may lead to erroneous conclusions about the long-term ability of grazinglands to sustain productivity when changes in species composition are minor and changes in soil nutrient levels are negative and large, or may lead to an overestimate of the impact of grazing when the opposite occurs. Assessment of grazing impact in ecosystems must be multiscaled.

1.3.8 Microeconomic Indicators

Livestock producers in areas where there are severe climatic conditions have limited options for improving their productivity compared with those in tropical areas. In all cases, much depends on size of operation, management skills, and economics of input/output relationships. In virtually all cases small-scale producers, especially very small ones, are severely constrained in technology adoption by lack of facilities.

The results of treating cows and heifers for intestinal worms definitively show that the poorer the nutrition level, the more benefit from treating for worms. Thus, in years when feed is short, analysts would recommend that special care be taken to carry out a good worming program. Likewise, cattle on poor-quality pasture should be systematically wormed to obtain the highest possible benefits.

Milk production and animals sold can be expanded by feeding concentrates to lactating cows, increasing minerals and molasses fed, using more fertilizer on pasture, and paying more for contracted labor. The problem is that changes like these require much more of a business orientation, a change which many smaller, more subsistence-oriented producers are not willing to make.